1. Field of the Invention
The present invention relates to methods for evaluating and controlling a lithography apparatus used in manufacturing a semiconductor device.
2. Description of the Related Art
In recent years, process control of lithography steps have become important due to miniaturization of process dimensions. As one of the process control, it is known to control an exposure dose and focus independently by separating factor of dimensional distortion of a pattern to be formed on a wafer (dimension variation factor) into an exposure dose variation and a focus variation (Jpn. Pat. Appln. KOKAI Publication No. 2001-102282).
Here, the exposure dose means not only a setting exposure dose on an exposure equipment but also an exposure dose called effective exposure dose. The effective exposure dose is obtained by converting factors having influence for pattern dimensions on a wafer into the exposure dose. The factors are, for example, error of mask, and resist process such as a application, bake or development.
In recent investigations, the following result is reported. The result suggests that the influence upon the resist dimensions differs between temperature variation of post exposure bake (PEB) and the other factors relating to the factors of dispersion of the effective exposure dose. Specifically, the difference appears in a dimensional variation due to optical proximity effect (which appears in space dependency of line pattern dimensions). More specifically, relating to the dimensional difference between dimensions of dense line and dimensions of isolated line, the dimensional difference is large when the exposure dose at the time of exposure is changed, but the dimensional difference is small when the heating temperature at the time of PEB (PEB temperature) is changed.
The change in the exposure dose (exposure dose variation) and the change in the PEB temperature (PEB temperature variation) prevent accurate formation of a fine resist pattern. Therefore, it is important to accurately evaluate the exposure dose variation and the PEB temperature variation, and then reflect the evaluated results in the control of the lithography apparatus.
However, in the conventional technique, the lithography apparatus is evaluated by using an effective exposure dose variation which is obtained without separating the exposure dose variation and the PEB temperature variation. In addition, a technique which accurately separates the exposure dose variation and the PEB temperature variation, and then measures the respective variations has not been proposed.
That is, the conventional technique has not proposed a method for evaluating the lithography apparatus by separating the effective exposure dose variation into the exposure dose variation and the PEB temperature variation.